Arsenic (As) – Periodic Table (Element Information & More)

This is a SUPER easy guide on Arsenic element.

In fact, the table mentioned below is the perfect information box (Which gives you every single detail about the Arsenic element in Periodic table.)

So if you want to know anything about Arsenic element, then this guide is for you.

Let’s finish this very quickly.

Arsenic Element (As) Information

Appearance	Grey metallic surface
State (at STP)	Solid
Position in Periodic table	Group: 15, Period: 4, Block: p
Category	Pnictogens
Atomic number or  Protons	33
Neutrons	42
Electrons	33
Symbol	As
Atomic mass	74.922 u
Electrons arrangement or  Bohr model	2, 8, 18, 5
Electronic configuration	[Ar] 3d10 4s2 4p3
Atomic radius	185 picometers (van der Waals radius)
Valence electrons	5
1st Ionization energy	9.815 eV
Electronegativity	2.18 (Pauling scale)
Crystal structure	RHO (Rhombohedral)
Sublimation point	887 K or 615 °C or 1137 °F
Density	5.73 g/cm3
Main isotope	75As
CAS number	7440-38-2

Arsenic in Periodic table

Arsenic element is in group 15 and period 4 of the Periodic table. Arsenic is the p-block element and it belongs to Pnictogens group.

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Why is Arsenic in Group 15?

Do you know, how many electrons can be accommodated in the first shell, second shell, third shell, fourth shell, etc…?

Here is the table showing the capacity of orbits to hold electrons. 

Number of electrons in shells.

Orbit / Shell (n)	Maximum no. of electrons this orbit can hold
K shell, n = 1	2 × 1² = 2
L shell, n = 2	2 × 2² = 8
M shell, n = 3	2 × 3² = 18
N shell, n = 4	2 × 4² = 32

Thus, 

• 1st shell can hold 2 electrons.
• 2nd shell can hold 8 electrons.
• 3rd shell can hold 18 electrons.
• 4th shell can hold 32 electrons.

Now the atomic number of arsenic (As) is 33.

Hence the arsenic element has electrons arrangement 2, 8, 18, 5.

This electron arrangement indicates that the outermost orbit of Arsenic element (As) has 5 electrons.

Hence, it lies in group 15.

Why is Arsenic in Period 4?

Let me ask you a question.

How many shells does arsenic have?

It’s 4. Right? 

You have already seen the bohr model of arsenic atom in the above table.

From the Bohr model, it can be found that the number of orbits or shells in arsenic is 4. Hence, as arsenic has 4 orbits, it lies in period 4 of the Periodic table. 

Why is Arsenic in p-block?

Before knowing this reason, first of all I want to ask you a simple question.

How can you determine the blocks-wise position of elements?

The simple answer: The elements will lie in the s, p, d or f block will completely depend upon the subshell in which the last electron will enter.

For example; the electron configuration of arsenic is [Ar] 3d¹⁰ 4s² 4p³. 

So the last electron of arsenic enters the p-subshell or p-orbital. 

Hence, arsenic is the p-block element.

7 Interesting facts about Arsenic

Interesting facts about arsenic element are mentioned below.

1. The word “Arsenic” was derived from the Persian word “Zarnikh” which means “yellow orpiment”.
2. Arsenic is the 53^rd most abundant element found from the earth’s crust.
3. In the earth’s crust, the proportion of arsenic by weight is about 1.8 ppm (parts per million).
4. On the earth, arsenic is mostly found in the igneous rocks.
5. In some countries like India, Taiwan, South America and Pakistan the groundwater flowing over arsenic rich rocks may contain high concentrations of arsenic in it.
6. Pure arsenic and its compounds are toxic. Arsenic was used as a poison.
7. Arsenic has adverse effects on health that causes damage to organs like the immune system, skin, nervous system, excretory system, etc.

Properties of Arsenic

The physical and chemical properties of arsenic element are mentioned below.

Physical properties of Arsenic

Physical properties of arsenic are mentioned below.

• At standard atmospheric pressure, arsenic directly transforms from solid to gaseous state. This is known as the sublimation process. Arsenic does not come into liquid state at standard atmospheric pressure, but it does exist in a liquid state under high pressures.
• The sublimation point of arsenic at standard atmospheric temperature is 615 °C.
• Arsenic has natural as well as many other radioactive isotopes, but out of them only one isotope is stable (i.e ⁷⁵As).
• The atomic mass of arsenic is 74.922 u and its density is 5.73 g/cm³.

Chemical properties of Arsenic

Chemical properties of arsenic are mentioned below.

• Arsenic is an element that shows the properties of metals as well as nonmetals. Hence it is classified as a metalloid on the periodic table.
• When arsenic is heated in the presence of air, it gets oxidized and it releases odour similar to that of garlic.
• If arsenic containing minerals are struck hard with a hammer, they release characteristic odour.
• The electron configuration of arsenic is [Ar] 3d¹⁰ 4s² 4p³, which indicates that the last electron enters the p-orbital. Hence, arsenic is a p-block element.

Uses of Arsenic

Uses of arsenic are mentioned below.

• Grey arsenic is a very good conductor of electricity. Hence it is used in industries.
• Arsenic is used as an alloying metal with lead to form a harder and durable metal.
• Gallium arsenide is a compound of arsenic that is used in lasers which produces light when electric current is passed through it.
• Arsenic is also used as a doping agent in devices like transistors.
• Although arsenic is a poisonous element, it is used in manufacturing insecticides.
• Arsenic is also used to prevent wood degradation by termites and fungus.
• In earlier days, arsenic compounds were used in bronze to increase its hardness.

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External resources:

1. Arsenic – Element information, properties and uses | Periodic Table. (n.d.). Arsenic – Element Information, Properties and Uses | Periodic Table. https://www.rsc.org/periodic-table/element/33/arsenic
2. P. (n.d.). Arsenic | As (Element) – PubChem. Arsenic | as (Element) – PubChem. https://pubchem.ncbi.nlm.nih.gov/element/Arsenic
3. Arsenic – Wikipedia. (2018, February 25). Arsenic – Wikipedia. https://en.wikipedia.org/wiki/Arsenic
4. The Facts on Arsenic | Dartmouth Toxic Metals. (n.d.). The Facts on Arsenic | Dartmouth Toxic Metals. https://sites.dartmouth.edu/toxmetal/arsenic/the-facts-on-arsenic/
5. What is Arsenic? – Arsenic – University of Maine. (n.d.). What Is Arsenic? – Arsenic – University of Maine. https://umaine.edu/arsenic/what-is-arsenic/